The problem of viral escape is a major challenge for those attempting to control an ongoing HIV-1 infection with AAV-delivered transgenes. This problem can be addressed by anticipating and blocking viral escape pathways. Alternatively one can target unvarying cellular proteins. In Project 4, we determine if antibodies targeting two HIV-1 coreceptors, CCRS and CXCR4, can safely control HIV-1 replication. MSM Protein Technologies, Inc. has proprietary technology for developing fully human antibodies that can recognize any CCRS or CXCR4 epitope, and for further improving these antibodies to obtain affinities in the picomolar range. We have generated antibodies against a range of chemokine receptors, using technology that we originally developed to study CCRS and CXCR4. However, antibodies recognizing chemokine receptors can interfere with appropriate immune function. It is therefore critical that antibodies targeting CCRS or CXCR4 are not themselves receptor agonists, and that anti-CXCR4 antibodies do not interfere with chemotaxis or signaling mediated by the CXCR4 ligand CXCL12/SDF-1a. We will therefore: 1) generate and characterize sets high affinity antibodies specific for CCRS, recognizing distinct and noncompeting epitopes, which do not agonize the receptor, but which efficiently inhibit HIV-1 infection. 2) determine if heterodimeric forms of these anti-CCRS antibodies more effectively neutralizing HIV-1 than any individual anti-CCRS antibody. 3) develop and improve an anti-CXCR4 antibody that efficiently inhibits replication of X4 and RSX4 HIV-1 isolates, but which does not compete with SDF1a binding to CXCR4. 4) evaluate the ability of these antibodies, delivered as AAV expressed transgenes, to control ongoing SHIV infections in rhesus macaques. These aims will generate several very high affinity anti-CCRS and -CXCR4 antibodies that potently neutralize HIV-1 infection, and establish their ability to control viral replication in vivo.